Gas lubricated seals have been used for many years in compressors and, in some applications, have largely replaced more conventional seals, including liquid lubricated seals. Since the sealing faces of gas lubricated seals are not in dynamic contact, properly designed gas lubricated seals offer significant benefits of reduced frictional torque and reduced heat generation compared to conventional seals. Moreover, since the high pressure gas supplied to a gas lubricated seal may be selected for its inert qualities in view of the application, and since a properly designed gas lubricated seal offers a long life, these seals are ideal for applications requiring complete emission control and process purity. In more recent years, gas lubricated seals have been applied to pump technology to seal between the rotating shaft sleeve and the pump housing. Accordingly, pump manufacturers have desired improved gas seals for various pump sealing applications.
One type of gas seal uses circumferentially spaced grooves in one of the sealing faces. The spiral grooves each extend radially inward from an outer periphery of the respective sealing face. Pressurized gas is supplied to these grooves to block the escape of the fluid being sealed. One such gas lubricated seal which is embodied in a cartridge design is the Type 2800 seal manufactured by John Crane, Inc. Other types of gas lubricated seals with spiraling grooves are disclosed in U.S. Pat. Nos. 4,423,879; 5,246,295; 5,385,409; 5,498,007 and 5,713,576. Other variations of gas lubricated seals are disclosed in an article entitled "Analysis of Spiral-Groove Face Seal for Liquid Oxygen" by Shapiro et al., published in ASLE Transactions, Volume 27, 3, pp. 177-188. Another type of non-contact gas seal marketed by A.W. Chesterton Co. as the 4400 TwinHybrid Gas Seal utilizes radially inward and outward sealing faces with the pressurized gas being supplied through the stationary ring and to circumferentially spaced elongate grooves spaced radially between the sealing faces.
While various types of double gas seals have been devised, the prior art has failed to effectively benefit from double gas seal technology. Prior art coplanar double gas seals do not provide effective lift off of both the radially outer sealing face and the radially inner sealing face under various conditions. Also, much of the prior art relating to double gas seals provide seal designs which are too large for many applications since the seals have a long axial length or require a considerable diametral space.
The disadvantages of the prior art are overcome by the present invention. An improved double gas seal is hereinafter disclosed which provides effective lift off of the radially spaced sealing faces and reliably seals pressurized fluid while minimizing seal wear.